The increasing density with the resulting finer design rules of semiconductive elements in integrated circuit devices increases the susceptibility of the devices to impurities which deleteriously affect the properties of the devices. Of particular concern are metallic precipitates in the silicon wafer in which the circuit is formed. Such precipitates can cause emitter-collector shorting in bipolar transistors, source-drain shorting in MOS transistors and a softening of the reverse breakdown characteristic of junction diodes.
While gettering techniques are available for elimination of undesired impurities in the silicon bulk, such techniques have limitations. Additionally, in some instances, such impurities (typically gold) are useful in solution in the silicon, for example, for reducing the lifetime of minority carriers in the base of bipolar switching transistors operated in saturation. The gold doping effectively improves the switching time of the transistor. In such a device it is important to keep the metal in solution in the silicon rather than as precipitates capable of forming conductive shorts (pipes). Additionally, it is desirable to be able to remove metallic precipitates from semiconductor wafers which have already had diodes and/or transistors and possible other circuitry fabricated therein and thereby to improve the quality of the p-n junctions included and to limit undesired shorting of components.